This invention relates to drill string by-pass valves, circulation valves employed in bore-hole drilling for oil and gas. In such valves, a circulation port is provided, whereby when pump circulation of drilling fluid is substantially reduced when the drill bit is "off bottom" or discontinued during "tripping", drilling fluid present in the drill string is discharged from the drill string through a port in the valve into the bore hole annulus. When pump circulation of drilling fluid to the bit is again started, a sleeve in the valve is displaced so as to close the by-pass port and permit circulation through the nozzles which are provided in the drill bit for circulation up the annulus to the surface. See U.S. Pat. No. 3,005,507, which illustrates such a valve known as a dump valve and U.S. Pat. Nos. 3,989,114 and 4,298,077 which illustrate a by-pass valve when circulation under pump pressure continues. Such valves are termed dump valves when they are used to insure discharge of fluid above the bit when no circulation is induced by the pump as in "running in", that is, assembling the drill string or disassembling the drill string, by a procedure known as "tripping". Such by-pass valves are termed "circulation valves" when they function when drilling is discontinued and the drill string is lifted off bottom and circulation is caused to discharge through the by-pass valve under reduced pressure.
While such by-pass valves are used in ordinary rotary drilling, where the entire drill string is rotated, they are also used when the drill is rotated by an in-hole motor mounted at the end of the drill string adjacent the bit particularly motors rotated by the circulation of the drilling fluid passing through the valve to the bit.
The by-pass valves are particularly useful in connection with the positive displacement motors such as described in U.S. Pat. Nos. 4,298,077, 4,220,380 or 3,989,114.